In laparoscopic procedures performed in the abdomen, working space is provided by insufflating the abdomen using a pressurized gas, such as carbon dioxide. The gas pressure, typically about 15 mm Hg, raises the abdominal wall by several inches, which provides a space into which instruments can be inserted through trocar tubes for visualization and to perform surgical procedures. To prevent the insufflation gas from escaping, each trocar tube forms a gas-tight seal with the abdominal wall, and with the instrument passed through it.
Instruments for use in laparoscopic surgery in which insufflation is used must also be gas tight to prevent the insufflation gas from escaping. A number of laparoscopic instruments, such as clip appliers and forceps, have two components passing through the trocar tube, an outer tube on which a static part of the instrument is mounted, and an operating rod that operates the moving part of the instrument. The operating rod is mounted inside the outer tube and must be capable of freely moving axially relative to the outer tube. Alternatively, the operating rod may operate two opposed moving parts, and the static part may support the moving parts.
The outer tube is shaped to form a gas-tight seal with a trocar tube, but, absent a suitable seal, the space between the operating rod and the outer tube provides a path for insufflation gas to escape through the instrument.
Two-component laparoscopic instruments also include a handle to which the outer tube is attached, and an operating lever, pivoting in the handle, to which the operating rod is connected. Moving the operating lever relative to the handle moves the operating rod axially, and operates the moving part of the instrument.
It is known to provide a grease seal between the outer tube and the operating rod. U.S. Pat. No. 5,100,420 shows the operating rod of a clip applier passing through a closely fitting rectangular aperture in a sealing block installed in the outer tube. The space between the operating rod and the sealing block is filled with silicone grease to prevent insufflation gas leaking between the operating rod and the sealing block.
A grease seal mounted in the outer tube has several disadvantages. A grease seal is short lived; the seal may start to leak after as few as twenty operating cycles. An instrument having a grease seal cannot be re-used, because the grease seal cannot be autoclaved. U.S. Pat. No. 4,027,510 shows a clip applier with a pair of sealing rings. Each sealing ring is placed in an annular groove in a widened portion at opposite ends of the operating rod. The sealing rings slide with the operating rod relative to the outer tube to provide a gas-tight seal between the operating rod and the outer tube.